Anterior Sub-Tenon’s Anaesthesia (ASTA) for Cataract Surgery Dr S Wu. FACRRM, FRACGP Dr KC Tang. FRANZCO, Clinical lecturer School of Rural Health, University of Sydney

Ocular regional blocks 1 = Anterior Sub- Tenon’s Anaesthesia (ASTA) 2 = Steven’s sub- Tenons Technique. 3 = Retrobulbar 4 = Peribulbar Introduction

Tenon’s Capsule Like a glove for the whole eye Starts at the limbus and lid muscles Initially fused to conjunctiva Loose matrix Follows sclera around the globe Sleeves around rectus and oblique muscles Attaches to optic nerve sheaths

Posterior instrumentation unnecessary for Sub-Tenon’s (ST) Block McNeela et al (2004) N=59 Successful ST blocks 6mm ultra-short cannula Kumar et al (2004) N=151 compared 3 sub-Tenon’s cannulae lengths: 25mm18mm12mm Sub-Tenon’s space accessed anteriorly!!! Sub-Tenon’s space accessed anteriorly!!! Short cannula achieved similar anaesthesia and akinesia

Needle sub-Tenon’s injection Ripart et al (1996) N=151 Unlike cannula ST techniques 25G needle without dissection Medial canthus sub- Tenon’s injection Mean depth 15-20mm 92% - total akinesia Dissection not necessary for sub-Tenon’s block

Ripart (1998) CT images of fresh cadavers 9mls contrast given by MC sub-Tenon’s injection spread to: Episcleral space Optic nerve sheath Rectus muscle sheath Lid muscles- orbicularis occuli & levator palpabrae Subconjunctival space

Short needle 25G 16mm

Methods Case series 60 adult elective cataract patients All received ASTA by author Using 2 common local anaesthetics 30 – lignocaine 2% +hyalase 30 iu/ml 30 – bupivacaine 0.5% + lignocaine 2% + hyalase 30 iu/ml Approved by regional HERC ANZCTR

Preparation Routine pre op care Supine, eye pillow ½ strength iodine Head stabilised by nurse Amethocaine 1% x1 drop Optional light sedation (midazolam)

ASTA Technique Outline Lift upper lid, look down Pierce conjunctiva and Tenon’s capsule in upper outer quadrant 5-7mm from limbus Advance needle about 5mm supero-medially Following curve of sclera Visually check needle position by forming a small bleb of L.A. Inject L.A. VERY SLOWLY, guided by patient comfort

Vol. 6-10mls, diff in each patient, guided by 3 signs of filling up the ST space as described by Ripart : Mod. proptosis + lid fullness + mod. chemosis

At the end of ASTA injection, complete lid drop evident

Excess chemosis Mostly resolves with gentle massage

Akinesia Scored 10min post ASTA, using Aggregated Motility Score (AMS) Validated scale used by Kumar, MaNeela, Brahma etc Lid + Globe mvt in 4 directions: up, down, medial, lateral 0 = no mvt 1 = twitch <1mm 2 = partial mvt 3 = full mvt Total akinesia = 0, adequate akinesia < =4, max mvt = 15

Pain Rated as it occurred during operation Numeric Verbal Rating Scale 0 = no pain 1-3 = mild 4-6 = moderate 7-9 = severe 10 = worst

Results Mean age 74, equal gender. All successfully completed surgery without supplemental anaesthesia No major anaesthetic complications No surgical complications due to ASTA Main complication = Sub conjunctival haemorrhage in 5% pts. 48% on warfarin or antiplatelet Rx 48% on warfarin or antiplatelet Rx

Akinesia 10min post ASTA 95% - AMS ≤4/15 100% - lid paralysis : levator palpabrae and orbicularis occuli

Pain during operation 58/60 pain free 2 patients- Transient mild pain 1-2/10 End of procedure No supplementation required

Discussion ASTA comparable to other sub-Tenons blocks Akinesia - 95% AMS ≤ 4 Learning curve McNeela et al (2004) 98% AMS<4 Kumar 3 cannulae (2004) % AMS<4 Koh et al, Concord Hosp, 2005, Steven’s sub-Tenon’s block Akinesia - 88% AMS≤4 Anaesthesia – 7% needed topical amethocaine supp.

ASTA - Comprehensive all-in-one block Relatively large volume Av = 9mls (similar to Ripart) One injection delivers LA to: Lid muscles, no need VII inj. Sub-conjunctival space Muscle sheaths Episcleral space Retrobulbar space

Implications for Safety ASTAAnterior Visually guided Short needle Less invasive – no dissection Improve Aesthetics & healing Reduce infection Avoids vulnerable anatomy Optic and other nerves CSF Blood vessels Retina / macula Should be safer

Potential Advantages Globe perforation Anterior Peripheral retina Visible Haemorrhage - anterior SeenCompressed No need to stop Warfarin or antiplatelets ?Safer in axial length ≥ 26mm Equipment is cheap & readily available – beneficial for developing nations Easily topped up anytime ?Role in patients with difficult access Previous surgery Adhesions Scleral buckles

Conclusion Small study ASTASimpleEffectiveSafe Phaecoemulsification cataract surgery Further research to elucidate its wider application

“Simplicity is achieving maximal effect with minimal means” Dr Kawana Zen Garden Master. Contact: